Process of manufacturing tungsten carbide



June 30, 1931. o. L. MlLLS PROCESS OF MANUFACTURING TUNGSTEN CARBIDE Filed Jan. 21, 1930 INVENTOR COI'Jf/S %0% K?,

A TTORNEY Patented June 30, 1931 UNITED STATES PATENT OFFICE OS CAB L. MILLS, OF LOS ANGLES, CALIFORNIA, ASSIGNOR TO MILLS ALLOYS ING., OF LOS ANGELES, CALIFORNIA, A. CORPOR-.ATION OF DELAWARE PROCESS OF MANUFACTURING TUNGSTEN CAIRBIDE Application filed January 21, 1930. Serial No. 422314.

My present invention relates to the production of tungsten carbide.

This application is a continuation in part of my copending application, Serial No.

371540, entitled Electric arc furnace electrode holder, and filed June 17, 1929, now Patent 1,77 5,437 issued' September 9, 1930.

Tungsten carbide is now commonly used 'as diamond substitutes for drll bits. When 1 manufactured under proper conditions, it is substantially pure and of a fine silky grainstructure having a hardness comparable, with that of a diamond.

In my former Patent No. 1,719,558, issued July 2, .1929, I descrbe an electric arc turnace, in which tungsten carbide of a hgh grade can be made in commercial quantities. My present invention relates to a method of manufacturing. tungsten carbide, especially by the aid of such an electric arc furnace, although the process is not limited thereto.

It has been observed that tungsten will absorb carbon to form the tungsten carbides. In my former patent hereinabove referred to, I make it possible to control the absorption of carbon by bringing the mixture acted upon by the arc, rapidly to the melting point; and immediately casting it rapidly in cool molds, whereby the chemical unon of tungsten and carbon is prevented, by the speed of cooling, from being re- Versed. My present invention relatesto a variation of the manner of use of the furnace disclosed in that patent, although the same attributes thereof are essential; that is, a rapid, uniform heating of the mix.

In my former patent, I am enabled to secure this-rapid, uniform heating by the use of a comparatively shallow crucible or work container placed beneath a vertical upper electrode made of carbon, the upper electrode being large enough at least to cover the work container completely; and the'arc voltage being maintained at such a low value that the tip of the electrode is closely spaced from the work and serves to confine the heat to it. This tip has also been noticed as being maintained remarkably blunt during operation, it

7 being maintained during operation at about the same area as the area of the work container below it.

These are now well understood phenomena. The arc being enclosedin a comparatively small chamber, it maintains the tem perature of the Work in the container without material losses by conduction, or through the walls,-or by radiation.

In my present invention, I may utilize these same instrumentalites or others which have equivalent efi'ects upon the work in the container. In making tungsten carbide, I

- have found that when the arc is placed upon a mass of finely divided tungsten, some carbon can be absorbed from the carbon atmosphere in the arc itself, but this absorption is not enough to yield a high grade alloy. In my former Patent, No. 1,721,966, issued July 23, 1929, I describe how this can be corrected by the use of scrap material. It is an object of my invention to make it possible to control the absorption of carbon in a simpler manner than disclosed in my prior patent.

It is another object of my invention in general to improve the product by roper manipulation of the arc furnace itsel My invention possesses many other advan- Lages, and has other objects which` may be made more easily apparent from a consideration of one embodiment of my invention. For this purpose I have shown a form in the drawing accompanying and forming part of the present specification. I shall now proceed to descrbe this form in detail, which illustrates the general principles of my in-. vention; but it is to be understood that this detailed description is not to be taken in a. limiting sense, since the scope of my invention is best defined by the appended claims.

Referring to the drawing:

The sin le figure is a diagrammatic sketch of an arc urnace by the aid of which my invention can be practiced.

' In this figure, I show a confined arc chamber 1, formed as by refractory walls 2. This arc chamber has an opening 3 at the top which rather closely encompasses a large upper electrode 4, which is movable vertically into the arc chamber 1 by any desred mecha- 1. Preferably there is a bed of loose carbon particles 8 in the bottom of the chamber 1.

Disposed on this bed of carbon 8 and directly beneath the upper electrode 4 is a work container 9, in which the mix'that I shall hereinafter describe, is disposed for treatment by the arc. A large opening 10 is also provided not only to View the operation of the arc, but also to make it possible to insert and withdraw the work container 9 as required in the operation of the process.

The current can be supplied to the arc from mains 11 and 12, connected to the clamps 5 and 7. The arc is formed between the blunt tip 13 of the upper electrode 4 and the material in the container 9. The space between this blunt tip and the top of the container 9 is maintained small in value, so that an arc df about 30 to volts alternating current is produced; and also so that no great heat uct can be made when the tungsten powder less occurs by direct radiation from the arc to the walls of the furnace or up toward the roof. The sloping point 14 of'the upper electrode 4 also serves by reflection or reverberaton to return heat to the lower part of the chamber where it isneeded, and to prevent too great a less of beat by conduction from the work through the bed 8.

In operation, the work container or crucible 9, which is also made of carbon, is first filled with the mixture; and then it is disposed beneat-h the electrode 4. The arc is then struck by lowering the upper electrode 4 onto the container 9, the current then flowing through container 9, and the carbon bed 8 to i the lower electrode structure 6. As soon as the arc is struck, the upper electrode 4 is moved upwardly a short distance. The arc is permitted to play on the work until all of the work is melted, and sometimes for a time in excess of that period, as determined-by exrience. With a container 9 of about 2 nches in diameter and about 1% inches or 1 .inches deep, the time required for melting the work is in the neighborhood of one minute. The upper electrode 4 is made 4 or 5 inches in diameter; It is thus seen that it is considerabl larger in diameter in the present instance than the work container 9, so as to cover, and indeed to overlap the work container 9. After the work has bee fully treated, the container 9 is quickly rem ved' as by a pair of pincers, and the content thereof i are poured mto comparatively cool molds.

In this process, about a pound of material is melted at a time, and the resulting material' has a fine silky structure of extreme hardness.

In making tungsten carbide, it Would appear that finely divided tungsten, such as tungsten powder, would be all that would be needed to make a good product. I find, however, that with an electric arc, there is an insuficient amount of carbon absorption that is possible in the short interval of operation. This, of course, could be corrected by proper manipulation, but in order to ensure a quick absorption of carbon and thereby speed up the production, I mix with the tungsten powder, some grains of tungsten carbide. The proportions are about twenty-four parts by weight of the tungsten carbide, to about six parts by weight of the tungsten powder. Preferably the tungsten carbide is in the form of crushed material, small enough to pass an 8 mesh screen. A small portion of this tungsten carbide can be still finer, say of suflicient fineness to pass a 30 mesh screen. In one form of `mix which I find advantageous, I use twenty pounds of crushed tungsten carbide fine enough to pass an 8 mesh screen, and three pounds of crushed tungsten carbide fine enough to pass a 30 mesh screen. To this is added six pounds of commercially pure tungstenpowder.

-Indeed, I find that a suficiently good prodof carbon during the Chemical combination,

fully to carburize' the tungsten powder n the mix, and especially when this mix is subjected to a carbon vapor, as in a carbon electric arc. Thus the deficiency of the carbon absorbed by the tungsten powder from the carbon vapor is compensated for by the addition of the tungsten carbide, since this carbide also absorbs carbonj The manipulation of the urnaceto maintain the blunt surface 13 hovering over the 'container 9 serves to maintain this blunt surface of substantially the same area as the container 9. It serves thereby to define the conical annular surface 14 which shields the upper part of the furnace from the action of destructive heat rays.

-I claim:

l. The process of manufacturng tungsten carbide, which comprises placing tungsten material from which the carbide is to be made in an open shallow work container, covering substantially all the exposed area. of the material with the arcing end of a carbon electrode, and maintaining a short arc between the electrode and the material.

2. The process of manufacturing tungsten carbide which' comprises placing a mixture of divided tungsten and divided tungsten caro bide in an open shallow work container and maintaining a short arc between the exposed material and a carbon electrode that has an arcing surface substantially eovering the whole exposed area, of the material.

3. The process of manufacturng tungsten carbide which comprises placing a. mxture of divided tungsten and divided tungsten carbde in an open shallow work container and maintain'ng a short are between the exposed material and a carbon electrode in such manner that the are acts upon substantially the whole exposed area of the material uniforml 4. he process of manufacturng tungsten carbide which comprises placing tungsten material from which the carbide is to be made, in a shallow open work container, and maintaning a short arc between the exposed ma- V terial and a carbon electrode in such manner that the arc acts upon substantally the whole ex osed area, of the material uniformly.

n testimony whereof I have hereunto set my hand.

OSCAR L. MILLS. 

